Apparatus for recording sound on



sflpt. 22, 1942 THOMPSON Re. 22,183

APPARATUS FOR RECORDING SOUND ON THIN DISKS Origingl Filed Dec. 15, 1958ll Hl'll I I INVENTOR 28 it l. v 01 7' I fir/9' ATTORNY Reis aued Sept.22, 1942 APPARATUS FOR RECORDING SOUND ON THIN DISKS Lincoln Thompson,Cheshire, Conn.,

The Sound Scriber Corporation,

minor to Stamford,

Conn., a corporation of Connecticut Original No. 2,200,866, dated May14, 1940, Serial No. 245,944, December 15, 1938. Application for reissueDecember 17, 1941, Serial No.

Claims.

This invention relates to sound recording, and more particularly to anapparatus for recording sound on a thin disk record.

It has hitherto been considered impractical to make sound recordings ona thin flexible disk due to the fact that the surface of said' diskwould become permanently deformed and would warp so badly that it wouldnot play back with satisfaction. Even when relatively thick aluminumdisks of the order of .030" thickness (20# gauge) were embossed withsound grooves in the conventional recording machines, it was found thatthe disks showed some warpage after recording. This was due largely tothe fact that the disk was mounted on a soft felt or yieldable rubberpad which permitted the heavy pressure of the embossing stylus (10 to 16ounces) to bend the disk record into "dish form. With thinner disks,this dishing or'warping effect would naturally be greatly aggravated.

By means of the present invention, the above and other disadvantageshave been overcome, and it has been found possible to emboss soundgrooves in an extremely thin flexible disk record without appreciablewarpage, using disks as thin as .006". This result has been accomplishedby eliminating the soft felt or rubber pads previously used as africtional foundation for the disk record, and in placing the recordupon a solid and rigid turntable or plate mounted on said turntable. Thetendency to produce warpage is still further reduced by employing alower embossing pressure on the stylus, whereby a more shallow groove orsound track will be produced. At the same time, in order to drive thethin record without slippage, an interlocking connection is made betweenthe of the record for fitting over a similarly shaped section on saidspindle.

By the use of this construction the thin record is supported rigidly sothat it cannot bend below record and the spindle of the turntable, as by.providing a square driving recess in the center may be recorded whichwill not buckle up during recording when positively driven by the centerspindle and without the necessity of clamping the record on theturntable.

A still further object of this invention isto provide an apparatus forrecording on a. thin semi-rigid metal disk which will be relativelyinexpensive to manufacture, simple in construction, ornamental inappearance, and very efficient and durable in use.

With these and other objects in view, there have been illustrated on theaccompanying drawing two forms of sound recording apparatus in which theinvention may be conveniently embodied in practice.

In the drawing:

Figure 1 illustrates partly diagrammatically the first form of improvedsound recording apparatus embodying the present invention.

Figure 2 is a top plan view of the thin disk record as it appears wheninterlocked with the turntable spindle, and with the embossing stylus inoperating position.

Figure 3 is an enlarged side view, partly in section, of the thin diskrecord turntable and embossing stylus shown in Figure 2, taken on theline 3-3 of Figure 2.

Figure 4 is a greatly enlarged sectional view of the disk record,turntable and stylus in operating position.

Figure 5 illustrates a fragmentary side view of a modified form of theinvention employing a rigid record supporting plate resting on the usualturntable felt cushion.

Referring now to the drawing wherein'like reference numerals denote likeparts throughout the several views, the numeral. i0 designates'aturntable which is adapted to be rotated by an electric motor II in theconventional manner. The motor H is adapted to be energized by beingconnected to a source of electrical energy through main line conductorsl2 and I3, a plug I I4, conductors l5 and I6, and a switch IT.

The sound grooves are adapted to be embossed in the record by means ofan electrically actuated recording head is arranged to swing over theturntable l0 and being driven in this swinging movement by power drivenmechanism, not shown. A suitable mechanism for this purpose wasdisclosed in my prior Patent No. 2,133,596, dated October 18, 1938. Thesound vibrations received by the apparatus are reproduced in the form ofa spiral groove in the disk record 24 by means of an embossing stylus iscarried by the recording head II, the latter being responsive to anelectrical circuit which includes a microphone 20, a pair of conductors2|. a vacuum tube amplifier 22, and a pair of conductors 23. Therecording head I! is of a conventional type, and is adapted to rest uponthe surface of a disk record 24 with a pressure of about four ounces.

The disk record 24 is preferably made from a thin flexible metal, suchas sheet aluminum, having a thickness of less than .015", and preferablybeing previously annealed at a temperaure of approximately 300 degreesF. to soften it and relieve it of all strains. The resultant disk 24 maybe termed semi-rigid," when com- ..pared with ,the conventional hardrigid disks previously employed, which were generallyat least .030" inthickness and unannealed. The diameter of the disk 24 may be chosen asdesired, and preferably should be such that the record will not buckleduring handling or recording. For example, if a disk .006" in thicknessis used, it has been found that for most efficient results the recordshould not exceed '7 inches in diameter.,

In order to drive the thin semi-rigid annealed aluminum disk record 24while, being embossed with sound grooves 25 (Fig. 4) withoutappreciablewarping, the center spindle 26 of the tumtable II is interlocked withthe center opening 21 in said record. For this purpose the spindle 26 ismade square in cross-section, and fits snugly within the opening 21which is also made of the same square shape. The turntable i is providedwith a flat, smooth, hard and rigid top surface 28, thus preventing theembossing stylus from producing warpage in the record 24 during therecording operation.

In order to produce more shallow grooves which may be more closelyspaced (such as 160- 200 grooves to the inchlthan was previouslypossible, the pressure of theembossing stylus on the record shouldpreferably be about 4 ounces, as compared to the high recordingpressures 16 ounces) formerly employed.

same

side of the disk record 24 without appreciable warping.

In operation, the stylus l8 forces up a pair of lateral ribs 3| and 32,which define the side borders of the sound groove and materiallyreinforce the stiffness of the record.

If desired, the blank disk record 24 may have a ring-shaped marking area33 etched upon its surface within the sound grooves for permitting theuser to make any desired indicia or memoranda thereon with a pencil.Three rectangular shaped marking portions 34, 35 and 35 may also beetched on the record for receiving any other desired indicia pertainingto the sounds recorded thereon.

It has also been found that if desired, the operator may write directlyacross the sound grooves with a pencil without harming said grooves oraffecting the reproduction of the sounds recorded thereon.

, when the record is used for receiving dictation of correspondence, inwhich case the thin record may be clipped to the copy of the lettertranscribed therefrom.

While there have been disclosed in this 4 specification two forms inwhich the invention If the record embossed in accordance .with theapparatus herein disclosed were played back in the usual form ofreproducing machine employing high pickup pressure and the hard metal orsapphire needles, the grooves would be rapidly torn and the recordirreparably damaged.

Applicant's thin soft metal records may, however, be readily reproducedwithout injury when played back on a reproducing apparatus, such as thatshown in applicants copending application, Serial No. 74,919 forPhonograph reproducers, died April 17, 1936, Patent No. 2,141,804,issued December 2'7, 1938. The apparatus disclosed in that applicationemployed a low inertia pickup with the usual hard sapphire needle whichexerts less than one-half ounce pressure on the record, andconsequently, the wear on the grooves is negligible. Moreover, the lowinertia pickup described in that atent permits the sound tracks to bereadily followed by the needle without Jumping grooves or.repeating ofgrooves.

may be embodied, it is to be understood that these forms are shown forthe purpose of illustration only, and that the invention is not to belimited to the specific disclosures, but'may be embodied and modified invarious other forms without departing from its spirit. In short, theinvention includes all the modifications and embodiments coming withining claims.

Having thus fully described the invention, what is claimed as new andfor which it is desired to secure Letters Patent is:

1'. Ih a sound recording apparatus, a disk record of thin flexiblesemi-rigid material of less than .015" in thickness, a flat hardsurfaced plate for directly receiving and rigidly supporting saidrecord, a rotating center spindle associated with said plate and havinga driving con- .nection with said record, and a swinging arm locatedabove said record and having a cutting head for indenting laterallyundulating helical grooves in said record without substantial warping.

2. In a sound recording apparatus, a disk record of thin flexiblesemi-rigid soft annealed aluminum of less than .015" in thickness, aflat hard surfaced plate for directly receiving and rigidly supportingsaid record, a rotating center spindle associated with said plate andhaving driving connection with said record, and a swingingarm locatedabove said record and having a cutting head for indenting laterallyundulating helical grooves in said record without substantial warping. V

3. In a sound recording apparatus having a movable stylus-carryingrecording arm, a disk record of thin flexible semi-rigid material havinga thickness between .006 inch and .030 inch, a hard surfaced rotatableplate directly receiving and rigidly stationarily supporting saidrecord,

a center driving spindle for said record normal to said plate, and meansforming a driving connection between said spindle and said record.

the scope of the follow- 4. In a sound recording apparatus having amovable stylus-carrying recording arm, a disk record of thin flexiblesemi-rigid material, a hard surfaced rotatable plate directly receivingand rigidly stationarily supporting said record, a center drivingspindle for said record normal to said plate, and means forming adriving connection between said spindle and said record.'

5. In a sound recording apparatus, a disk record of thin flexiblesemi-rigid material, a hard 6 22,1ss- .7 '3 surfaced plate rotatable onan axis at right angles to said record for directly receiving saidrecord, said record vlying incontact with said plate throughout itssurface and being stationarily supported thereby so as to rotate as aunit therewith, said plate having a driving connection with said recordand a movable arm carrying an indenting stylus to record a laterallyundulating groove on the surface of said record.

' LINCOLN THOMPSON.

